During the first year of this study, all monkeys were randomized into study groups for a cross over design evaluating the acute effects of 3 different monkey diets: standard NIH chow, the NIA 1-87 diet, and the WI Harlan Teklad chow. The latter two diets are used at the respective sites for long-term studies of calorie restriction effects on function, morbidity, and mortality. For baseline and each 3-month timepoint, the following measures were collected: body weight, morphometric measures, body composition scan, pulse wave velocity for arterial stiffness, glucose tolerance test, biopsy of liver, fat and muscle, and banked serum and plasma samples. All monkeys are in the final stage of the study.